Insulation is used on wire for a wide variety of purposes, including protecting the wire from inadvertent or accidental contact with other conductors. The type of insulation which is used will depend upon a wide variety of factors including: economy, ambient temperature, desired flexibility, space limitations, the environment, the applied potential, atmospheric conditions, ambient contaminants, and a wide variety of other conditions with which those familiar with the art are acquainted. It is not unusual to provide an insulation which is a combination of a variety of insulators. For example, there may be an initial insulation of some type of fiber covered by either a plastic or rubber. Sometimes, the outer insulation includes a braided metllic sheath or flexible metal conduit. Some of the more common insulating materials include: woven fiber such as cotton, linen, nylon or hemp; rubber or any of the plastics having similar or improved characteristics for the application under consideration; and a variety of other substances and/or combinations as currently used in the industry.
In order to make electrical connection to the insulated wire, it is necessary to strip or remove a portion of the insulation near the end of the wire in order to expose the bare wire for making a connection thereto by any of a wide variety of methods including: soldering connections, crimping terminals, welding, compression under a screw or other device, and any of a variety of other techniques with which those familiar with the art are aware.
Removing the insulation to prepare the wire for electrical connection may be done by any of a wide variety of means including manual and automatic. The techniques disclosed herein relate to automatic removal of insulation and, more particularly, but not exclusively, to the removal of insulation from relatively small wire such as size 16 down to wire sizes in the 20's and smaller.
There are two common methods which are customarily used in automated procedures for removing a predetermined length of insulation from an end of a wire. One method requires the cutting of the insulation and the stripping thereof from the wire. The other method employs the application of heat to cut, burn or melt through the insulation and then the stripping of the severed insulation from the wire. As a general rule, the cutting procedures are faster than the thermal procedures.
Cutting the insulation and stripping it from the wire requires a very careful adjustment to avoid any possibility that the cutters may nick the wire. Nicking the wire is detrimental as it seriously weakens the wire and introduces the increased probability of the wire breaking. Accordingly, it is customary to adjust the cutters so that they do not quite cut through the entire insulation. The cuts may be through approximately 65 to 90 percent of the insulation thickness. Thereafter, the wire is gripped on both sides of the cut and the insulation at the free end is stripped off by an application of longitudinal force. The force must be sufficient to rupture the uncut portion of the insulation and to overcome the frictional force between the wire and the insulation. Depending upon the type of insulation material used, the rupturing of the uncut portion may result in a necking down of the insulation rather than leaving a square shoulder. In certain applications, a square shoulder is highly desirable in order to help provide a shoulder stop as the wire is pushed through a hole, such as in a circuit board, for soldering. Also the necking down and/or the resultant stretching of the insulation results in an exposed length of wire of somewhat indeterminate and variable length.
The structure disclosed herein is designed to overcome the necking and other disadvantages of the prior art cutting and stripping techniques.